Environmental Impact Analysis of Solar Power Generation Process
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W. Khaenson, S. Maneewan and C. Punlek / International Energy Journal 17 (2017) 113 – 124 113 Environmental Impact Analysis of Solar Power Generation Process Using Multicrystalline and Amorphous Silicon Solar Cells in Thailand www.rericjournal.ait.ac.th Wasin Khaenson*, Somchai Maneewan*1 and Chantana Punlek* Abstract – This paper presents the results of the environmental impact assessment into two different technologies for the production of solar power in Thailand. It considers mass and energy flows over the whole power generation process and compares two types of silicon solar cell; multicrystalline and amorphous. The process operations that make up the system are the solar cell array, inverter stations, transformer stations, a control center and substations. This study also examines the economic feasibility of such power stations, by analyzing their investment costs and the internal rate of return (IRR). After analyzing the results, 1 kWh of solar power generation was found to have an impact upon both human health and ecosystem quality, whilst resource depletion was unaffected. When the overall impact was compared against the non-renewable power generating technologies of natural gas, combined cycle and coal-fired power stations, solar energy was found to have an appreciably lower environmental impact, with the multicrystalline plant having the lowest impact of all. However, the economic analysis revealed that, despite their low environmental cost, under the present market conditions both solar power technologies are not financially viable. Keywords – Amorphous silicon, life cycle assessment, multicrystalline silicon, solar cell power plant. 1. INTRODUCTION consumption was 2,895 ktoe, an increase of 4.4% on the same time the previous year. Heat energy consumption Solar energy is the conversion of sunlight into electricity. accounted for the greatest share, 1,798 ktoe of the total It is also among the cleanest and most abundant energy final renewable energy consumption, followed by sources available. The process uses photovoltaic cells electricity, and biofuels (ethanol and biodiesels) which (PV) to convert light into an electric current using the measured 661 ktoe, and 436 ktoe, respectively. Of this photovoltaic effect [1]. A solar cell, or photovoltaic cell final renewable energy, solar energy accounted for 98 (PV), is a device constructed from materials which ktoe or 686.33 MW of the power generated, an increase exhibit the photovoltaic effect - a unique property where of 18.07% from the previous year. This has resulted in electrons are released at the atomic level when exposed both a decrease in energy imports (amounting to to photons of light. These newly freed electrons can be 1,257.34 million baht), and also a decrease in CO collected by creating a positive/negative imbalance 2 emission (amounting to 0.3 million tons) [6]. Although within the cell, resulting in an electric current and thus all forms of solar energy can potentially decrease CO electricity. When a number of these cells are connected 2 emission, the other environmental impacts can vary together, they form a photovoltaic module which can depending on the technology used to construct the produce electricity at a certain direct current voltage. photovoltaic module. Since the current generated is directly dependent upon The task of this paper is to carry out a comparative the amount of light hitting the module, they are study of the main environmental impacts of power generally wired together in giant arrays in order to generated from solar energy, at each stage of the process. maximize the electricity produced [2]. There are various The environmental impact is measured using life cycle different designs of solar cells, differing in the type of assessment (LCA). This is a technique that evaluates the materials used to construct the semi-conductor (the part environmental impact of each stage of a product’s life, of the cell which undergoes the photovoltaic effect). from cradle to grave, thus enabling a quantitative Crystalline silicon (c-Si) is by far the most common estimation of its environmental impact at every stage of choice, and is used in almost 90% of photovoltaic cells its life cycle [7]. The LCA provides a comprehensive today [3], [4]. However, a growing market is that of thin view of the various environmental aspects of the product film solar cells, which includes amorphous silicon (a-Si), or process, thus creating a more accurate picture of the cadmium telluride (CdTe), and copper indium gallium environmental trade-offs in product and process diselenide (CIGS) [5]. selection, and ensuring a more accurate decision making Thailand’s solar energy can potentially be process [8], [9]. The four stages of the LCA are: (1) generated in significant quantities because of the Goal and scope definition, (2) Life cycle inventory country's tropical location. In the first quarter of 2017 (LCI), (3) Life cycle impact assessment (LCIA), and (4) (January to March), the final renewable energy Interpretation [10]-[12]. Finally, in addition to the environmental aspects, economic analysis has been *Department of Physics, Faculty of Science, Naresuan University, undertaken to ascertain the financial viability of Phitsanulok, 65000, Thailand. constructing and operated solar power plants under 1Corresponding author; current market conditions. Tel: +665 596 3552. E-mail: [email protected]. www.rericjournal.ait.ac.th 114 W. Khaenson, S. Maneewan and C. Punlek / International Energy Journal 17 (2017) 113 – 124 2. EXPERIMENTAL SET UP plant in northern Thailand using multicrystalline silicon solar cells, generating 90 MW, and one in central 2.1 Goal and Scope Definition Thailand using thin film amorphous silicon cells, This study assessed the environmental impact and generating 55 MW. Both plants were the largest in their economic viability of the solar power generating process respective regions. The most important specifications resultant from the two leading types of solar cell module are given in Table 1. The electricity generated was sold in Thailand, using the life cycle assessment. Two solar to the Electricity Generating Authority of Thailand cell power plants were studied as shown in Figure 1; one (EGAT) and Provincial Electricity Authority (PEA). Fig. 1. Site of solar cell power plants studied. 2.2 Functional Unit • Solar cell array: This process consisted of solar cell modules which were wired together to form an The functional unit used for this study was 1 kWh of array. Erecting the arrays required significant power generated by the solar cell power plant. The amounts of land. They converted the solar energy environmental impact results were calculated in terms of directly into electricity utilizing the photovoltaic Pt per functional unit of 1 kWh. effect. 2.3 Allocation • Inverter stations: Inverters changed the direct This study focused solely on the solar power generation current (DC) from the solar cell array process into process. Other stages, such as the manufacture or alternating current (AC). recycling of the solar cell modules were not taken into • Transformer stations: Transformers were used to account. increase or decrease the voltages of alternating current to the appropriate level. 2.4 System Boundaries • Control center: The control center monitored and The process of solar power generation was subdivided controlled all processes for generating electricity, into five system boundaries; the solar cell array, inverter from the solar cell array through to the substations. stations, transformer stations, a control center and • Substations: Substations connected and switched substations [13]-[15]. The process studied is shown in the electricity lines, and changed the voltage using Figures 2 and 3. Details of the five subsystems are transformers. provided as follows: www.rericjournal.ait.ac.th W. Khaenson, S. Maneewan and C. Punlek / International Energy Journal 17 (2017) 113 – 124 115 Table 1. Specifications of solar cell power plants studied. Description Northern solar cell power plant Central solar cell power plant General The average annual power generated 139,446 MWh 109,054 MWh Total power consumption 762 MWh 565 MWh Total water consumption 20,043 m3 5,729 m3 Power plant area 296 hectares 192 hectares The average annual solar radiation 5.18 kWh/m2/day 5.55 kWh/m2/day Solar module Cell type multi-Si multi-Si multi-Si multi-Si a-Si a-Si Maximum power (Pmax) 245 W 250 W 245 W 250 W 128 W 135 W Open-circuit voltage (Voc) 37.1 V 37.2 V 37.3 V 37.4 V 59.8 V 61.3 V Short-circuit current (Isc) 8.63 A 8.69 A 8.73 A 8.83 A 3.45 A 3.41 A Maximum power voltage (Vmp) 37.1 V 30.3 V 29.9 V 30.1 V 45.4 V 47 V Maximum power current (Imp) 8.63 A 8.27 A 8.19 A 8.31 A 2.82 A 2.88 A Expected lifetime 25 years 25 years 25 years 25 years 25 years 25 years Installed number 157,300 98,098 57,200 196,196 456,750 108,864 Inverter Rated output power 500 kW 250 kW Rated output voltage 340 Vac 440 Vac Rated output current 860 Arms 328 Arms Rated input voltage (DC) 586 Vdc 600 Vdc Efficiency ≥98% ≥95% Installed number 180 220 Transformer Rated voltage (kV) 22 22 22 22 22 22 22 115 Rated power (kVA) 50 100 160 250 1,250 1,250 2,500 50,000 Rated frequency (Hz) 50 50 50 50 50 50 50 50 Installed number 3 6 1 1 90 1 27 2 Fig. 2. The system boundary of power generation from solar energy. www.rericjournal.ait.ac.th 116 W. Khaenson, S. Maneewan and C. Punlek / International Energy Journal 17 (2017) 113 – 124 Fig. 3. Electrical single line diagram. 2.5 Life Cycle Impact Assessment (LCIA) had notably different results. This is because the multicrystalline plant required an electrical input, and The Eco-indicator 99 (H, A) end-of-point impact this resulted in the emission of nitrogen, oxygen, water assessment method was also used in the analysis.